The invention concerns a pipe arrangement having two pipes joined at their ends by way of a coupling device.
Coupling devices of this kind for joining pipe ends are available in a variety of embodiments.
For example, it is known to use, for the joining of pipes, sleeve-shaped press fittings which for purposes of creating a pipe join are slid over the pipe ends and then radially pressed together, both the press fitting and the pipe being plastically deformed. Pipe joins of this kind and the associated press fittings are described, for example, in DE-C-11 87 870 and EP-B-0 361 630.
It is furthermore known, from DE-A-33 10 027, to equip the pipe ends with conical indentations in order to increase the retention forces by way of the resulting wedge effect.
In addition, special coupling devices are used in which the two pipe ends are clamped in annular spaces which are formed between an internal support sleeve and an external pressing sleeve surrounding the latter and made of metal. In this context, the pipe ends are fastened in the coupling device by the fact that the pressing sleeve is pressed radially inward, resulting in plastic deformation and in clamping of the pipe ends between the pressing sleeve and support sleeve.
It is possible in this context to allocate a separate pressing sleeve to each pipe end, as is known from DE-U-90 16 310; or to use a single, continuous pressing sleeve as proposed in EP-A-0 582 543.
The known coupling devices have proven entirely successful in practice. They are often problematic to use, however, if they are exposed during operation to large temperature fluctuations, since large forces can then act on the join due to temperature-related expansions of the pipe and coupling device. In the case of coupling devices which are used to join synthetic-resin pipes in hot-water lines, for example, the operating temperature fluctuates in the range from 20 to 100 degrees C., and temperature changes of this kind result in length changes in the pipes of approximately 20 mm per meter of pipe length. The metal coupling devices expand very little by comparison, so that the join is exposed to large constraining forces, which can cause the pipe ends to slip in the coupling device and can cause the join to leak.
In order to counteract this problem, it is proposed in GB-A-1 213 786 to equip the pipes with bellows-like regions which absorb the length changes of the pipe and are thus intended to relieve the load on the connecting point. Provision is also made, in the annular space between two pipe ends inserted into one another, for a sealing element which is capable of at least partially compensating for radial expansions. Thermal expansions can partially be compensated for with this embodiment, but this achieved at the cost of the disadvantage that in order to adapt to the temperature differences which occur and to the overall pipe length by which the resulting expansions are determined, the pipes must possess different bellows regions. In other words, a large variety of pipes is required, which entails a large outlay.
It is therefore the object of the invention to create a pipe arrangement which easily guarantees reliable and leakproof joining of two pipe ends even in the presence of large temperature fluctuations.
According to the present invention, this object is substantially achieved by a pipe arrangement having at least two pipes joined at their ends by way of a coupling device, the coupling device having at least one pressing sleeve slid onto the pipe end and press-joined to the pipe end, and there being provided between the pressing sleeve and pipe end an elastic region which possesses an elasticity, and is configured, such that thermal axial and radial expansions of the pipe end occurring during operation are absorbed by elastic deformation of the elastic region, without slippage of the pipe end in the pressing sleeve.
With this pipe arrangement expansions of the pipe resulting from temperature changes or other stresses are thus absorbed by the elastic region, which is configured in elastic fashion such that it can deform in accordance with the pipe expansion which occurs without impairing the nonpositive join between the pressing sleeve and the respective pipe end. In this context, the elastic region should be configured so that both thickness changes and length changes of the pipe end pressed into the coupling device can be absorbed.
Advantageously, the elastic region is configured so that the tensile and transverse elasticity increases in the direction of the free end of the pressing sleeve. As a result of this feature, the deformation behavior of the elastic region corresponds to the longitudinal expansion behavior of a pipe retained in the coupling device, so that expansion of the pipe is greatest in the region of the free end of the pressing sleeve, and is practically nonexistent at its axial end inserted into the pressing sleeve, since the longitudinal forces have already been absorbed by then.
In order to achieve a transverse elasticity which increases in this fashion, it is possible to provide, in the surface of the elastic region facing the pipe end, slits extending in the circumferential direction, whose depth and/or breadth increases in the direction of the free end of the pressing sleeve.
According to one embodiment of a pipe arrangement according to the present invention, the pressing sleeve is constituted by a plastically deformable outer sleeve, which for example can be made of metal, and an elastically deformable annular element, held in the outer sleeve, which is hereinafter referred to as the xe2x80x9cinner sleevexe2x80x9d even though it does not have the rigidity of a sleeve in the conventional sense. The inner sleeve is advantageously made, like the pipes, of synthetic resin. This ensures that the pipe end and the inner sleeve deform to approximately the same extent.
In a further embodiment of the invention, the outer sleeve and the inner sleeve can also be of conical configuration, so that the inner sleeve can be slid into the outer sleeve from the free end of the pressing sleeve, and the inner sleeve can additionally be pressed into the outer sleeve while elastically deforming a spring element, in order to create the necessary press-join between the pressing sleeve and pipe end. This creates a detachable join, since the outer sleeve does not need to be plastically deformed.
The inner sleeve can also be constituted by a plurality of inner sleeve elements axially adjacent to one another and provided separately from one another. The inner sleeve elements then advantageously have a T- or L-shaped cross section, thus forming slits that are open toward the pipe end when they are axially lined up with one another. The individual inner sleeve elements can be made, for example, of metal.
According to a further embodiment, the pressing sleeve comprises an elastically deformable synthetic-resin element with plastically deformable fibers or annular elements, made of metal or synthetic resin, embedded therein. In this case the pressing sleeve is configured as an injection-molded part so that it is easy to manufacture. The desired elasticity of the pressing sleeve is attained by way of the synthetic resin, while fastening of a pipe end is accomplished by way of the fibers or rings, by pressing then inward accompanied by plastic deformation, thereby press-joining the pipe end and pressing sleeve to one another.
With this embodiment, the desired increase in longitudinal or transverse elasticity in the direction of the free end of the pressing sleeve can be attained by the fact that the pressing sleeve has a wall thickness which decreases toward its free end. Alternatively or additionally, slits can provided in this case as well in the inner surface of the pressing sleeve, to increase the elasticity.
In a manner known per se, there can be provided inside the pressing sleeve a support sleeve which forms with the pressing sleeve an annular receptacle for a pipe end. The support sleeve can also be configured elastically in the region of its outer surface coming into contact with the pipe end, so that it can absorb expansions of the pipe end by elastic deformation. For example, the pressing sleeve and support sleeve can be manufactured integrally as a synthetic resin part with plastically deformable fibers or rings embedded therein. In addition, both the support sleeve and the pressing sleeve can have a wall thickness which decreases toward their free end, and can have slits on their outer surface.
Alternatively, the pressing sleeve can be divided in its circumferential direction into several sleeve elements, which are joined to one another under the elastic preload of spring elements in such a way that the pressing sleeve can expand radially against the preload of the spring elements, and which are configured resiliently in the axial direction. With this embodiment, the desired elasticity for absorbing temperature-related expansions of the pipe end is achieved by the spring elements that are provided, and by the resilient configuration of the pressing sleeve. Advantageously, the sleeve elements are elastically compressed by compression spring elements, and in the axial direction have radial protrusions which can be elastically compressed and stretched.
According to a further embodiment, the pressing sleeve is made of an elastically deformable material and has a cavity which can be filled with pressing fluid in order to press-join the pressing sleeve to a pipe end by expanding the pressing sleeve. Alternatively, it is possible to provide in the cavity a powdered medium which upon excitation, in particular upon ignition or reaction with water, reacts by expanding and by spreading apart the pressing sleeve. The spreading of the pressing sleeve results here in the press-join between the pipe end and pressing sleeve. Advantageously, the pressing sleeve is surrounded by a fixed reinforcement sleeve, so that expansion of the pressing sleeve takes place substantially radially inward toward the pipe end that is to be fastened.